This invention relates generally to a system for rotating an antenna shaft to a predetermined position and maintaining said position. Devices of this nature are particularly suited and desirable for positioning directional antennas in order to maximize the desired signal strength and minimize undesired stray signals, noise, and reflected signals. For instance, to achieve reception of television signals of maximum strength, it is desirable that the main signal strength lobe of a directional receiving antenna be aligned along a straight line to the transmitting antenna and pointed at the transmitting antenna. Further, since television receivers are often capable of receiving signals from a multitude of stations, it is desirable that one have the ability to rotate the receiving antenna to the optimum position with respect to the chosen transmitting antenna. It is also desirable that antenna rotation be accomplished automatically and without personal attention in conjunction with the selection of a particular channel on a television or radio.
The orientation of the receiving antenna is a critical factor in optimizing the reception of television broadcast signals. Antenna rotors are particularly useful in areas where transmitting antennas are located in different directions with respect to a receiving antenna. Since television receivers are capable of receiving many different channels, it is especially desirable that the rotor system accurately and repeatedly position the antenna in the chosen direction in order to maximize the strength of the desired signal.
It is further desirable that the antenna rotor automatically rotate the antenna to the optimum direction upon the selection of the desired channel without making intermediate stops. The automatic rotation allows repeated operation without personal attention and the lack of intermediate stops provides for rapid antenna positioning. However, in many instances it is also necesssary that rotation be restricted in such a manner as to avoid a series of rotations in the same direction which might otherwise cause the antenna lead in wires to become wrapped around the rotor shaft and chafe or break. By automatically determining the direction of rotation, based upon a comparison of a signal representing the desired position and a signal representing the actual position prior to the energization of the rotator, one may restrict rotation as desired, avoid lead-in wire damage and still position the antenna quickly.
In light of these desirable properties for an antenna rotor system, one must also design the system for ease of attachment and operation with existing radio and television receivers. In systems utilizing predetermined channels such as television, the antenna rotor system disclosed herein may be interfaced with the channel selector to automatically position the antenna in response to channel selection.
The prior art is typified by rotor systems utilizing complex digital systems involving shift registers, memories, analog-digital converters, etc. These are designed to rotate an antenna at high speed with varying maximum drive rates and with no restrictions on the degree or direction of rotation. See for instance U.S. Pat. Nos. 3,448,360 issued to J. E. Pohl; 3,437,894 issued to J. E. Pohl; and 3,826,964 issued to F. Byrne. Systems of this nature are found, for example, in radar installations where the antenna position is constantly sensed and adjusted as quickly as possible to follow a moving object. Less sophisticated rotor systems are characterized by a proliferation of relays and switches used in conjunction with a manual control box incorporating mechanical, rather than electrical, position sensing, indicating, and control devices. These have often proven to be unreliable due to mechanical failures.